You can have which ever Primary you want but at least for now I prefer bola shot due to the stun and my items.

The Elemental Arrow in the form is insanely good vs the act 2 key warden and can be nice area damage to take out groups.

Vault is to get though/away from combat so any rune you want can be used here.

Impale will do the MOST damage here because it does double the normal damage for a crit (so if you have 300% crit damage extra it is 2x more damage overall)

Spike Trap can be very nice for kiting people and with that rune can go off 3 times so for the cost of 1 you get 3 mines in the same place for 3x overall damage for the one cast and still hits everything in the range of it.